The occurrence of many human cancers can be linked to impaired nonfunctional p53 protein. The p53 protein is a tumor suppressor encoded by a gene whose disruption is associated with about 50% of all cancers. The p53 protein acts as a checkpoint in the cell cycle, either preventing or initiating programmed cell death. Additionally, p53 protein is also involved in the development of tumors that have become resistant to treatment. It therefore appears that p53 plays a key role in the controlling the progression of cancer.
p53 is a transcription factor whose ability to initiate programmed cell death is most often repressed in cancer. Of the variety of biological molecules that are capable of inactivating p53, the oncoprotein MDM2 is believed to be the main negative regulator of this protein. Additionally, MDM2/p53 association has been implicated to play a role in drug resistance that has become a major problem in anti-cancer therapy.
The present invention provides methodology for selecting compounds that are capable of antagonizing the p53/MDM2 interaction. Additionally, the invention provides a strategy for overcoming negative regulator-dependant cancer resistance in vitro, cell-based, and xenograft models. Of the several classes of antagonists have been developed, the most prominent and best investigated are the nutlins.
Recently, another p53-binding protein, MDM4 (MDMX) has gained increasing attention as an equally important negative regulator of p53. In particular, a consensus exists that effective activation of p53-induced apoptosis must be based on a dual-action approach, involving both an MDM2 and an MDM4 antagonist. Thus, dual-action p53/MDM2/MDM4 antagonists “could be used to treat 2,000,000-3,000,000 new cancers each year, and so might represent an important class of anti-cancer drugs, assuming that their therapeutic index is acceptable.” Toledo & Wahl (2006). See Wahl et al., Nat. Rev. Cancer (2006), 6, 909.
Yet neither small molecular weight MDM4 inhibitors nor dual-action MDM2/MDM4 antagonists have been identified. Additionally, a high resolution structure of p53 bound to the MDM4 protein has not been published, which precludes the development of molecules capable of inhibiting or disrupting the p53/MDM4 interaction.